First of all, jacking up a car on an incline should never be your first choice.
As I understand it, the brakes worked fine; you jacked it up, put on the handbrake and now the drum won't come off. That's different than the more common problem of the shoes rusting to the drum after storage.
The missing screw would keep the drum from turning, or trying to fall off, but your problem is that neither the hub or the drum turn. Which I find puzzling if both wheels are off the ground. It should move by using a punch or that spark plug tool in the tool kit as a lever through the hole.
So back to the drum. Perhaps the handbrake is stuck full on and the shoes won't retract; or, the drum is cocked on the shoes. Look at the handbrake adjuster threads in front of the handle: with the handle down, are the adjuster nuts also retracted or sticking out? If not, wiggling the cables at the back might help. This will need to resolved later.
Now try to back of the brake adjusters. This may be difficult if they are rusted in place, since the normal cure requires access to the inside. So don't round the edges. Just spray with PB blaster a few times and give them a try.
You may have to force the drums off. When doing any of the following, wear safety classes!!
Start by beating around the drum on the area where the shoes rub. I've used a combo of whacking, then prying from the back. Just don't bend the backing plate too much. Pieces of drum have been known to break off/fly around.